Chapter 1: Why Food Is Processed

At first glance, the reasons why food is processed may seem obvious to some. It is often considered that food products are processed solely to extend their storage life or to reduce the risk of spoilage (Figure 1.1). However, there are additional reasons why foods are processed.

It has been estimated by various sources that one-third to one-half of the world's food supply is lost due to spoilage (Figure 1.2). Food losses in the United States of America have been estimated to be as high as 40% (Gunders, 2012).

Essentially, the quest to extend the storage life or “shelf-life” of a food product stems from a need to match supplies of food with the demands of time and space, or location.

In countries like Canada and the northern portions of the United States, the ability to grow food products is limited by the climatic conditions characterized by the four seasons of the year. During an appreciable portion of the year, it is too cold to grow crops. This means that crops harvested in the late summer or early fall must be maintained in a quality form for use throughout the winter and spring months until fresh produce can be obtained during the following year's growing season. Food processing allows these time-related needs to be addressed.

Apart from the growing season considerations, many consumers want foods that will simply last for a long time when stored in their pantries, on their kitchen shelves, or in their freezers. By processing foods such as fruits and vegetables when they are at their peak of quality and freshness, food processors can deliver products to meet these demands (Figure 1.3).

While certain areas of the world are enduring months of harsh climates, other portions of the world are enjoying much more temperate conditions. These countries may be able to harvest crops continuously, or may be able to grow two crops per year.

By exporting agricultural commodities, many tropical countries are able to sell their produce to an enthusiastic market willing to pay higher prices for fresh produce during the “off season”.

Food processing often plays a role in getting this food from one location to another while minimizing the loss of quality and nutrition, thereby addressing what we might describe as “space-related needs” (Figure 1.4).

Many of the things that are taken for granted during the winter months, including fresh tropical fruits, were not available prior to the end of World War II. It was not until controlled supply chains were developed to get these products from their sources to waiting markets that the potential for exports could be fully exploited.

Unfortunately, there are areas of the world that cannot produce enough food to feed their own populations during any portion of the year. Through drought or the encroachment of desert landscapes, there is not the water nor the soil fertility to produce sufficient amounts of food. At the same time, more distant nations may be enjoying bumper harvests and actually be experiencing food surpluses that go well beyond their foreseeable future needs. If these foods could be shipped to the areas in such dire distress, in a readily utilizable form that would be stable over time, both the spatial and time-related needs could be met. Fortunately, this is within the realm of possibility through the application of food processing technology.

Food processing also helps to ensure the cleanliness and safety of the world's food supply. Through the application of food processing, it is possible to reduce levels of microbial contamination that would otherwise create outbreaks of disease that could afflict millions.

Simply washing fruits and vegetables in clean, “potable” (i.e., drinkable) water is a good first step in any processing procedure (Figure 1.5).

Non-microbial contaminants and undesirable foreign materials are also routinely removed during processing (Figure 1.6).

Food that would otherwise spoil before it could even get to market is maintained in an edible form by minimal processing techniques that have little, if any, effect on the food itself.

Although many of us never really think about it, processing makes some foods edible that otherwise could not be digested in the human body. Examples of this include starch-based foods such as Irish potatoes. In their raw form, potatoes contain ungelatinized (granular) starches which humans cannot readily digest. However, by heating the potatoes in boiling water (or by other means), these starches are gelatinized. The gelatinized starches can then be digested (Figure 1.7).

Through food processing, consumers can experience variety, convenience, and diversity in their diets that was not possible in the past. Food science has provided flavours and forms of food that are convenient to use while meeting the expected quality levels of the consumer.

Time-impoverished families want, and can get, complete meals that are essentially ready to serve with little or next to no preparation. Store shelves and freezer compartments are lined with literally hundreds of products to satisfy the needs of families who no longer have the time to prepare a traditional sit-down dinner meal.

Instantized potato flakes (Figure 1.8) are available that reduce the time for preparing mashed boiled potatoes to a matter of minutes. This is in contrast to the time taken to peel the potatoes, cut them, boil them in water until fully gelatinized, and mash them for final use. With instantized potato flakes, the appropriate volume of flakes is mixed with the prescribed volumes of boiling water and milk. After mixing, the potatoes are ready to serve.

Microwavable meals or ready-to-eat meals from in-store delicatessens cater to these individuals and families (Figure 1.9).

A diversity of ethnic dishes that was unknown to preceding generations can now be enjoyed by today's consumer. As communications, world travel, and immigration have increased, so has the appreciation of the fine foods that are available in what were previously considered to be exotic locations. Food processing has brought the production of many “ethnic” foods to countries where they have now become favourites. Not only that, but they are available in convenient formats which may only require thawing and heating.

Food quality has already been mentioned several times. However, the attributes which go together to create an overall impression of quality have not been fully articulated. It is important not to confuse “quality” with “safety”. Although the terms are often used interchangeably, their actual meanings are quite different. We will discuss “food safety” in Section 1.3.

The following are some of the factors used to define food quality:

• Nutritional value

• Aesthetic aspects:

  • appearance/colour

  • taste/flavour

  • feel/texture

  • aroma

  • sound

  • etc.

• Functional properties:

  • gelation properties

  • thickening properties

  • water binding ability

The typical consumer most frequently judges quality on the aesthetic aspects which appeal to the five senses.

If a product doesn't look appealing, the consumer will reject it. If you envision an apple, you will have some pre-conceived ideas as to what it should look like. It should have a certain shape and colour, as well as being free from blemishes. The apple shown in Figure 1.10 has a pleasing red colour, a characteristic shape for this variety, and the peel is not marked.

In addition, the apple in Figure 1.10 may have an appropriate firmness, with a pleasant aroma, at the time of purchase. When consumed, it could provide the desired “snap” as you bite into it, as well as having the expected mouthfeel and taste. You should also experience an enhanced aroma as you eat the apple.

Up to this point, we have only examined the attributes of the apple that are detected by our five senses. There is no guarantee that the apple is nutritious. However, we tend to accept this on the basis of faith since we know that apples are generally considered to be nutritious.

In order to look at functional properties, we can look at starches that are often used in making gels or in thickening gravies.

The corn starch powder shown in Figure 1.11 is expected to contribute thickening properties when included in a gravy or sauce mixture. If it fails to do so, it is not meeting the quality standards of the user. To be a successful thickener, the starch must be ungelatinized prior to use. It needs to gelatinize within the mixture. In cases where the starch has been gelatinized prior to use, it will not do its desired task.

We can make similar observations about ingredients that are used in jams to bind water and create the gelling properties.

Quality aspects can be affected by deterioration over time, and other factors, which we will discuss later in this chapter.

Safety is a major concern among consumers. As mentioned above, “safety” is often confused with “quality”, or the two terms are simply lumped together.

Simply stated, a food material is considered as being unsafe to eat if consuming it will make you ill, or be harmful to you in any way.

It may seem strange, but a product of apparent low quality may be quite safe to eat - even though it may not be appealing to our senses.

While the apple in Figure 1.10 may be of extremely high quality, it may not be safe to eat. Let's suppose that the apple fell to the ground in the orchard while workers were picking them. There may have been cattle, goats, or other animals grazing under the apple trees prior to the harvesting. Grazing animals tend to leave their droppings behind which are contaminated with potentially harmful microorganisms.

Microorganisms could be transferred to the surface of the fallen apple due to brief contact with contaminants on the ground. If the apple was not properly washed prior to eating, the consumer could end up suffering from serious health issues.

In contrast, a less attractive apple could be totally safe to eat, yet not have all the apparent higher quality attributes.

We will discuss food contamination later in this chapter.

It is generally accepted that when any crop is harvested, or any product is manufactured, deterioration will begin almost immediately. While some degree of “aging” may enhance the quality of certain products such as wine or cheese, excessive or improper aging may render others useless. Most often, deterioration affects the quality of the food, but it can also have an impact on safety.

In order to reduce or eliminate the effects of deterioration over time, it is necessary to understand the basic causes of this undesirable process.

There are three basic methods by which food deterioration can occur.

Physical deterioration is often quite easy to detect visually or by feeling the food material. A good example of this is the loss or gain of moisture.

Let's consider a carrot which is bright orange and crisp at the time it is pulled from the ground. If you take the carrot in your hands and bend it, the carrot will probably break in half. At this stage, the moisture content of the carrot will be about 89% by weight.

If the carrot is not stored in a cool, moist environment, the loss of moisture can begin to occur. As the carrot loses moisture, it becomes more limp, or “flaccid”. If you were to bite into it, there would be no appealing crispness. The carrot would simply bend in your hands as shown in Figure 1.12.

At the opposite end of the moisture scale, we may have soda biscuits which are supposed to be very dry so that they break easily into small flake-like pieces. If these biscuits are exposed to humid air, they will absorb moisture and become soft, thereby losing their desired texture (see Figure 1.13).

Another example of physical deterioration is the reduction of particle size or breakage of products. This can occur during transportation where the product may be subjected to vibrations and bumping on rough roads. In Figure 1.14, a biscuit is shown in its broken state.

As its description implies, chemical deterioration is the result of undesirable chemical reactions occurring within a food material. One of the most common degradation reactions is with oxygen. There is approximately 20% oxygen in the air around us, so it is quite natural that it would enter into reactions with compounds present in the food.

The juices of citrus fruit such as oranges contain delicate flavour oils that provide a pleasant aroma and taste. If these oils react with oxygen, they can produce unappealing off-flavours and a brown discolouration (Figure 1.15).

Another example of oxygen causing the deterioration of a product is oxidative rancidity. In this case, oxygen reacts with fats or oils to create a noticeable off-flavour. This is particularly common when butter or cooking oil is left exposed to the air for prolonged periods of time (Figure 1.16).

Many chemical and biological reactions speed up with increases in temperature. Based on an equation developed by the physical chemist Svante Arrhenius in 1889, it is generally accepted that the rate of a chemical reaction will double if the temperature is increased from 10 °C to 20 °C. While this may not be exactly true for all reactions, it does provide a good indication of the effects of temperature on how fast a reaction can proceed. Using the opposite approach, it can be stated that the rate of a chemical reaction can be reduced by half if the temperature is lowered from 20 °C down to 10 °C.

The energy present in sunlight can change the chemical structure of compounds present in food materials. Some light-sensitive products are sold in brown bottles to protect the contents from the negative effects of sunlight.

If you have ever doubted the ability of sunlight to create chemical changes, take a look at the colour of fabrics, such as window curtains, exposed to the sun for prolonged time periods. You may also notice that their texture has changed and that the fabric no longer holds together very well. Even something as simple as a piece of newspaper can turn from white to a yellowish-brown due to prolonged exposure to sunlight.

Some degree of care must be taken so as not to confuse biological deterioration with biological spoilage, which will be discussed later in this chapter. In addition, there may be some degradative chemical reactions that are caused by biological processes.

One biological reaction that causes deterioration of quality involves the enzyme polyphenol oxidase. This reaction is particularly evident in cauliflower. Originally, the cauliflower florets are creamy-white in colour. However, with the passage of time, the naturally-occurring polyphenol oxidase present in the cauliflower can cause the development of brown, or even black, pigments. Figure 1.17 shows a fresh cauliflower and what it looks like after sitting at room temperature for approximately one week.

The growth of microorganisms is most often associated with contamination and disease.

Deterioration is what we call a “kinetic process”. This means that time plays a major role in many aspects of deterioration (Figure 1.18). It is a factor that must never be forgotten.

As a result, processors must minimize the time interval between the harvesting of a crop and its processing. With many perishable foods, or semi-perishable foods, the time interval between their processing and consumption is also important.

Food processors must understand these food deterioration mechanisms and be able to address them through the application of appropriate processing techniques. While it is essential that any process reduce or eliminate causes of deterioration, these same techniques must not create additional issues of safety or quality loss.

A simple way of looking at a contaminant is to consider it as being anything that should not be present in a food product. Even something that is generally recognized as safe (i.e., it has ‘GRAS’ status) can be a contaminant if it should not be in the product formulation. This is because it will not appear on the ingredient line of that product and may possibly cause harm to an unsuspecting consumer.

Physical contaminants are most often regarded as pieces of material that should not be present. These include things like small stones and pieces of metal as shown previously in Figure 1.6.

Depending on their size, physical contaminants can be removed by screening the incoming raw materials. Metal detectors can be used to detect the presence of small pieces of metal.

Dirt or soil clinging to the surfaces of fruits and vegetables is a very common contaminant (Figure 1.19). This soil may carry earth-borne contaminants with it as well. Fortunately, in most cases, it is relatively easy to remove.

The most problematic physical contaminant is broken glass (Figure 1.20). It is extremely hard to see and there are no simple methods available for detecting its presence in food products. For this reason, glass should be banned from all production areas, with the possible exception of the final packaging line where glass bottles may be the desired form of containment.

Contamination of food materials by various chemicals can happen along the entire food production continuum.

Pesticide and herbicide residues used for killing insects and weeds before the time of harvest can remain in the food and pose a health danger to consumers.

Improper storage and handling of such things as fertilizers on the farm, or chemicals in production facilities can lead to contamination of food products after harvesting (Figure 1.21). All chemicals must be stored in secure areas separated from food materials.

Chemicals used for sanitation and cleaning of the processing equipment warrant particular attention. Typically, acidic and basic (i.e., alkaline) solutions are employed, along with detergents and disinfectants to clean the interior surfaces of pipes and heat exchangers etc. Without thorough rinsing of these cleansing agents after use, or if pools of accumulated solutions remain after cleaning, there can be a carry-over of chemicals into products subsequently travelling through the system.

In liquid beverage processing systems which operate on a continuous basis and use automated cleaning procedures, there is a need to ensure that all chemical cleaning agents and solutions are flushed from the lines with potable (i.e., drinkable) water before introducing product for processing.

The effects of residual chemicals may range from creating off-flavours or odours, to posing a serious health threat to consumers.

Biological contamination is probably what first comes to mind when dealing with the subject of contamination. It is not difficult to envision mold growing on the surface of a tomato (Figure 1.22) or other food material.

Even more worrisome than the mold colonies which we can see with the naked eye, are the microorganisms that are invisible to us. Many of these are considered as being “pathogens” which are capable of causing disease or illness in humans.

As an indication of how small these microorganisms really are, there needs to be over one million of them present in one millilitre of water before the water becomes cloudy.

Due to their size and adaptability to a variety of conditions, these harmful microorganisms can be spread easily and can grow on many foods and food preparation surfaces.

Dealing with microbial growth and the destruction of microorganisms is a major field of study in its own right. Although we are not able to cover the topic in an exhaustive manner here, the chapter on “Thermal Processing” will provide some insight into how heat is used to destroy microorganisms in food products.

We also need to recognize that biological contamination is not limited to microbial growth. Insect infestations as well as the impact of small animals and birds can be included here (Figure 1.23). However, the end result of these intrusions on the food supply chain is often microbial contamination through feces etc.

Risks of biological contamination continue right through to the point of consumption. Improper storage of foods in the home and inadequate cooking or other incorrect preparation procedures may fail to destroy microorganisms that are present, or allow them to grow. Storage and reheating of left-overs can often be overlooked as potential situations for microbial growth.

Allergens are the fourth type of contamination that can be problematic to consumers, as well as to processors.

Within the general population, there are individuals with sensitivities to certain compounds. In these cases, there may be the development of a skin rash, sore throat, or joint pain, in addition to an upset digestive system.

Individuals with food allergies tend to experience much more violent or severe reactions to certain foods than those with food sensitivities. Allergies trigger responses from the body's immune system which can include anaphylaxis or “anaphylactic shock”. In these cases, there can be a tightening or constriction of the breathing passages, a sudden drop in blood pressure, dizziness, or loss of consciousness.

Based on information from Health Canada (Government of Canada, 2019), food materials or ingredients that are considered to be significant allergens include:

• Eggs

• Milk

• Mustard

• Tree nuts and peanuts (Figure 1.24)

• Seafood

• Soy derivatives

• Sulphites

• Wheat

• etc.

While it is not possible for processors to avoid using these materials in their products, it is important to declare all ingredients on food packages and to draw attention to potential allergens.

Some processors manufacture their products in facilities which are “peanut free”, and include a symbol on their packages to indicate this to the consumer (Figure 1.25).

Even though a product may not actually contain a food allergen, there are opportunities for cross-contamination of allergen-free products by other products in a production facility where allergens may be used. For this reason, it is imperative that processes be thoroughly cleaned between product runs to prevent the carry-over of potential allergens. Some manufacturers try to avoid this problem by incorporating phrases such as “may contain peanuts”, or other allergens on the labels of all their products. However, this does little to provide safe, high quality products to those with allergies or sensitivities who rely on label claims in their food purchasing decisions.

It is a common misconception that maintenance or enhancement of food quality is limited to within the confines of the food processing plant. In actual fact, quality is influenced by numerous factors along the entire food chain from a time even before the seeds of a crop are planted until the time the food is consumed.

More and more food processors are becoming mindful of the impact of raw material production and handling on their ability to manufacture high quality finished products. They are becoming acutely aware of the effects of distribution, handling, storage, and end-product preparation on the safety and quality of the products that the consumer eats. For this reason, there is an increasing tendency among food producers to adopt the approach of managing the entire food production and distribution chain.

Throughout the previous discussion, the importance of food processing has been repeatedly demonstrated. In conjunction with this, there is the need to be constantly aware of the fact that an underlying requirement of food processing is to maintain a safe and high quality food supply. Failure to acknowledge this fact can doom a processor to failure.